The invention relates to heating devices, and particularly, to gas heating devices. More particularly, the invention relates to safety circuits for controlling gas heating devices.
Gas-fired heating devices, such as water heaters, often include a combustion chamber and air plenum disposed below a tank, such as a water tank. A gas manifold tube, an ignition source, a thermocouple, and a pilot tube typically extend into the combustion chamber. When the temperature of the water in the tank falls below a set minimum, fuel is introduced into the combustion chamber through the gas manifold tube and a burner element. This fuel is ignited by a pilot burner flame or the ignition source, and the flame is maintained around the burner element. Air is drawn into the plenum via an air inlet, and mixes with the fuel to support combustion within the combustion chamber. The products of combustion typically flow through a flue or heat exchange tube in the water tank to heat the water by conduction.